LocalStorageVec

Useful links

• https://doc.rust-lang.org/std/

0. Intro

Let's create a resizable buffer called LocalStorageVec. Its elements live on the stack when there are only a few, but are moved to the heap when the LocalStorageVec length goes above a certain size. On the stack, elements are stored in a fixed-size array. On the heap they are stored in a dynamically-sized Vec.

1. General Structure

Our data structure representation will look like this:

#[derive(Debug, PartialEq, Eq, Clone)]
pub enum LocalStorageVec<T, const N: usize> {
    Stack { buf: [T; N], len: usize },
    Heap(Vec<T>),
}

We have two cases

• Stack: stores up to N values on the stack. len tracks how many of the elements of buf have a useful value.
• Heap: stores values on the heap

The T type parameter makes this data structure generic over the element type. The const N: usize parameter controls how many elements (at most) are stored on the stack. The N value must be known at compile time.

Step 2: Basic methods

Try running

cargo test test2

This should give the following output

running 3 tests
test exercise::test2::is_empty ... FAILED
test exercise::test2::len_capacity_vec ... FAILED
test exercise::test2::len_capacity_array ... FAILED

failures:

---- exercise::test2::is_empty stdout ----
thread 'exercise::test2::is_empty' panicked at 'not yet implemented', src/exercise.rs:73:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- exercise::test2::len_capacity_vec stdout ----
thread 'exercise::test2::len_capacity_vec' panicked at 'not yet implemented', src/exercise.rs:31:9

---- exercise::test2::len_capacity_array stdout ----
thread 'exercise::test2::len_capacity_array' panicked at 'not yet implemented', src/exercise.rs:31:9


failures:
    exercise::test2::is_empty
    exercise::test2::len_capacity_array
    exercise::test2::len_capacity_vec

Make these tests pass by implementing the functions of STEP 2.

Steps 3..=6

Like step 2, there will be a couple of skeleton definitions with todo!s and a module with tests that you can run with cargo test. Try to implement the todo!s so that the tests pass.

Step 7

We're into bonus territory here. Try to implement more functions from Vec for our LocalStorageVec. insert and remove are suggestions

Bonus

Read the documentation for MaybeUninit and try to use it to get rid of the Default bound on most functions.